Cooling circuit section and cooling circuit

ABSTRACT

Cooling circuit section (2), intended for the circulation of a refrigerant, said cooling circuit section (2) comprising:—at least two compressor assemblies (30), fluidically connected in parallel, each compressor assembly (30) comprising:—a compressor (40) configured to receive a low-pressure refrigerant having a first pressure, and for increasing the pressure of the low-pressure refrigerant so as to produce a compressed refrigerant having a second pressure that is greater than the first pressure, the compressed refrigerant comprising oil,—an individual oil separator (42) comprising an inlet (58) fluidically connected to the compressor (40) so as to receive the compressed refrigerant from the compressor (40), each individual oil separator (42) being configured to separate a first fraction of oil from the compressed refrigerant, the cooling circuit section (2) further comprising a common oil separator (32).

The present invention relates to a cooling circuit section and a cooling circuit.

The present invention in particular relates to the field of refrigeration units for commercial and residential applications.

U.S. Pat. No. 4,506,523 discloses a cooling circuit section for a refrigeration system comprising two compressors connected in parallel in a fluid manner. A common discharge header of the compressors is connected to a common oil separation system including an oil separator unit with an oil reservoir. Oil separated from the refrigerant in the separator unit and collected in the oil reservoir is returned directly into the compressors via an oil return line connecting the oil separation system to the compressors.

However, the cooling circuit section as described above has several drawbacks.

Indeed, the inventors of the present invention have found that, due to the particular structure of the system with only one common oil separator feeding the oil back into both compressors, the exact amount of oil fed back into each of the compressors is difficult to control. This can be detrimental for the safe operation of the compressors, which requires a sufficient amount of oil. Furthermore, the total amount of oil filtered from the refrigerant in prior art systems is not entirely satisfactory.

The present invention aims to resolve the aforementioned problems by providing a cooling circuit section with improved operational safety.

To that end, the invention relates to a cooling circuit section, intended for the circulation of a refrigerant, said cooling circuit section comprising:

-   -   at least two compressor assemblies, fluidically connected in         parallel, each compressor assembly comprising:         -   a compressor configured to receive a low-pressure             refrigerant having a first pressure, and for increasing the             pressure of the low-pressure refrigerant so as to produce a             compressed refrigerant having a second pressure that is             greater than the first pressure, the compressed refrigerant             comprising oil,         -   an individual oil separator comprising an inlet fluidically             connected to the compressor so as to receive the compressed             refrigerant from the compressor, each individual oil             separator being configured to separate a first fraction of             oil from the compressed refrigerant,         -   the individual oil separator further comprising:             -   a refrigerant outlet, through which the compressed                 refrigerant is intended to be discharged from the                 individual oil separator after separation of the first                 fraction of oil and             -   an oil outlet, through which the first fraction of oil                 is intended to be discharged from the individual oil                 separator, the individual oil separator being further                 configured to return the first fraction of oil to the                 compressor,     -   the cooling circuit section further comprising a common oil         separator fluidically connected to the refrigerant outlet of         each individual oil separator so as to receive the compressed         refrigerant from each of the compressor assemblies, the common         oil separator being configured to separate a second fraction of         oil from the compressed refrigerant.

According to advantageous but not mandatory aspects of the invention, such a cooling circuit section may comprise one or several of the following features, taken in any technically possible combination:

-   -   the common oil separator comprises an inlet, fluidically         connected to the compressor assemblies so as to receive the         compressed refrigerant from the compressor assemblies, a         refrigerant outlet, through which the compressed refrigerant is         intended to be discharged from the common oil separator after         separation of the second fraction of oil, and an oil outlet,         through which the second fraction of oil is intended to be         discharged from the common oil separator;     -   the cooling circuit section further comprises a common feedback         tube fluidically connecting the common oil separator to each of         the compressors so as to feed the second fraction of oil back         into the compressors;     -   the common feedback tube comprises an expansion valve configured         to decrease the pressure of the second fraction of oil from the         second pressure to the first pressure;     -   each compressor assembly comprises an individual feedback tube         fluidically connecting the oil outlet of the individual oil         separator to the compressor so as to feed the first fraction of         oil back into the compressor of the compressor assembly;     -   the individual feedback tube comprises an expansion device         configured to decrease the pressure of the first fraction of oil         from the second pressure to the first pressure;     -   the common oil separator is a coalescence oil separator or a         centrifugal oil separator;     -   each of the individual oil separators is configured to separate         the oil from the refrigerant based on differences in the         densities of the refrigerant and the oil;     -   the individual oil separators are chosen among a fluid speed         decrease oil separator, configured to decrease the speed of the         fluid fed into the oil separator and a fluid direction         modification oil separator, configured to change the direction         of the fluid fed into the oil separator;     -   the compressor of each compressor assembly is a hermetic         compressor;     -   the refrigerant is carbon dioxide, preferably carbon dioxide         R744.

The invention further relates to a cooling circuit comprising a cooling circuit section as described above, the cooling circuit further comprising a heat exchanger device configured to cool the refrigerant, an expansion valve and an evaporator device.

According to advantageous but not mandatory aspects of the invention, such a cooling circuit may comprise one or several of the following features, taken in any technically possible combination:

-   -   the heat exchanger device, the expansion valve and the         evaporator device are connected in series, the heat exchanger         device being connected to an outlet of the common oil separator         and the evaporator device being connected to an inlet of the         compressor assemblies;     -   the heat exchanger device is a condenser configured to cool the         refrigerant such that the refrigerant condenses into a liquid         state;     -   the heat exchanger device is a gas cooler configured to cool the         refrigerant such that the refrigerant remains in the gaseous         state.

The invention and other advantages thereof will become more clearly apparent in the light of the description which follows of an embodiment of a cooling circuit section according to the invention, only given as an example and made with reference to the appended drawings wherein:

FIG. 1 is a schematic diagram of a cooling circuit comprising a cooling circuit section according to the invention, and

FIG. 2 is a schematic diagram of an individual oil separator of the cooling circuit of FIG. 1.

FIG. 1 shows a cooling circuit 1 intended for the circulation of a refrigerant. In this figure, the intended circulation direction of the refrigerant in the cooling circuit is indicated by arrows.

The refrigerant is a fluid adapted for transporting heat from a volume that is to be cooled to an environment.

The refrigerant is of a type as known as such in the art. For example, the fluid is a hydrochlorofluorocarbon fluid. In another example, the refrigerant is carbon dioxide (for example R744). However, any other adapted type of refrigerant may be used.

As shown in FIG. 1, the cooling circuit 1 comprises a cooling circuit section 2.

The cooling circuit section 2 comprises an inlet tube 20, an outlet tube 22, and at least two compressor assemblies 30 and a common oil separator 32 disposed there-between.

The inlet tube 20 is intended for the circulation of a refrigerant having a first pressure and the outlet tube 22 is intended for the circulation of a refrigerant having a second pressure, the second pressure being greater than the first pressure. The compressor assemblies 30 are configured to increase the pressure of the refrigerant from the first pressure to the second pressure.

Preferably, the second pressure is strictly greater than the first pressure.

In the example of FIG. 1, the cooling circuit section 2 comprises three compressor assemblies 30. However, a different number of compressor assemblies 30 may be used depending on the needs.

The compressor assemblies 30 are fluidically connected in parallel. More particularly, each compressor assembly 30 is fluidically connected to the inlet tube 20 of the cooling circuit section 2 such that it receives at least a portion of the refrigerant circulating in the inlet tube 20.

Each compressor assembly 30 comprises a compressor 40, an individual oil separator 42 and an individual feedback tube 44.

The compressor 40 is for example hermetic compressor.

A hermetic compressor is a compressor in which the motor and the mechanical compression parts are arranged in a hermetically closed casing. The casing is more particularly a steel casing.

The only openings in the casing are the inlet 50 and the outlet 54 which are configured to receive or discharging the refrigerant. In particular, there is no additional opening for feeding additional fluids, such as oil, into the compressor.

The casing of the hermetic compressor is not configured to be opened.

The compressor 40 comprises an inlet 50 for the refrigerant, a compression unit 52 for compressing the refrigerant from the first pressure to the second pressure and an outlet 54 for the refrigerant.

Each inlet 50 is fludically connected to the inlet tube 20.

The first pressure depends on the application requirements. The first pressure is for example comprised between 12 and 60 bar, and typically equal to 28 bar.

The second pressure depends typically on the ambient air condition. The second pressure is for example comprised between 45 and 130 bar.

In the following, the refrigerant having the first pressure is referred to as “low-pressure refrigerant” and the refrigerant having the second pressure is referred to as “compressed refrigerant”.

The compression unit 52 of the compressor 40 comprises mechanical moveable parts (not shown) which are lubricated by oil. The oil is of any type adapted for the use in refrigerant compressors. It may be, for example, a mineral or a vegetable oil.

During the operation of the compression unit 52, a fraction of the oil used for the lubrication of the compressor 40 mixes with the refrigerant. Therefore, the compressed refrigerant exiting the compressor 40 at the outlet 54 comprises some oil.

The amount of oil introduced into the refrigerant is, for example, a function of the rotation frequency of the compressor 40 and/or of a working point of the compressor 40.

The individual oil separator 42 is configured to separate a first fraction of the oil contained in the compressed refrigerant and for returning this first fraction of oil into the compressor 40 through the individual feedback tube 44.

The individual oil separator 42 is fluidically connected to the compressor 40 so as to receive the compressed refrigerant from the compressor 40. In particular, an inlet 58 of the individual oil separator is fluidically connected, for example via a connection tube 56, to the outlet 54 of the compressor 40.

The individual oil separator 42 comprises, in the example of FIG. 2, a separation unit 59, a refrigerant outlet 60 and an oil outlet 62.

The individual oil separator 42 is configured to separate, in the separation unit 59, a first fraction of oil from the compressed refrigerant such that the first fraction of oil exits the individual oil separator 42 through the oil outlet 62 and the remaining compressed refrigerant exits the individual oil separator 42 through the refrigerant outlet 60.

The compressed refrigerant exiting the individual oil separator still comprises oil. More particularly, the amount of oil remaining in the compressed refrigerant corresponds to the amount of oil in the compressed refrigerant entering the individual oil separator 42 reduced by the first fraction of oil removed by the individual oil separator 42.

The individual oil separator 42 is of any type adapted to separating oil from a refrigerant.

According to one embodiment, the individual oil separator 42 is configured to separate the oil from the refrigerant based on the differences in the densities of the refrigerant and the oil.

According to one example, the oil separator 42 is a fluid direction modification oil separator, which is configured to modify the trajectory of the refrigerant so as to separate the lighter molecules from the heavier ones. In fact, when the trajectory of the fluid is modified, the heavier molecules in the fluid tend to continue, due to their inertia, on their initial trajectory, whereas lighter molecules tend to change their trajectory. The light molecules are thus separated from the heavy molecules. Such fluid direction modification oil separators are known in the art.

For example, the separation unit 59 of the individual oil separator 42 comprises a T-shaped tube comprising a main tube and two deviation tubes fluidically connected to the deviation tube. Each deviation tube extends substantially perpendicular to the main tube. A first deviation tube of the separation unit 59 is connected to the refrigerant outlet 60, while the second deviation tube of the separation unit 59 is connected to the oil outlet 62.

According to an alternative embodiment, the individual oil separator 42 is a fluid speed decrease oil separator configured to decrease the speed of the fluid received therein so as to separate the oil from the refrigerant. As known, the speed decrease of a considered fluid within the oil separator 42 depends on its density. Fluid speed decrease oil separators are known in the art.

In the example shown in FIG. 2, the individual oil separator 42 further comprises a casing 57 and an inspection glass 61. The inspection glass 61 comprises a glass inserted into an opening of the casing 57. The inspection glass 61 is configured to visualize the oil flow out of the individual oil separator 42.

As mentioned above, the individual oil separator 42 is configured to feed the first fraction of oil back to the compressor 40. In particular, the oil outlet 62 of the individual oil separator 42 is fluidically connected, via the individual feedback tube 44, to a tube communicating with the inlet 50 of the compressor 40.

In the example shown in the figures, the individual feedback tube 44 comprises an expansion device 63 configured to decrease the pressure of the first fraction of oil from the second pressure to the first pressure. In the example shown in the figures, the expansion device is an expansion valve. However, any other adapted expansion device may be used, for example a capillary tube.

The refrigerant outlet 60 of the individual oil separator 42 of each compressor assembly is fluidically connected to the common oil separator 32.

More particularly, each compressor assembly 30 comprises an individual connection tube 64 having an inlet connected to the refrigerant outlet 60 of the individual oil separator 42. The cooling circuit section 2 further comprises a common connection tube 66 having an inlet connected to an outlet of each of the individual connection tubes 64, and an outlet connected to the common oil separator 32.

As shown in FIG. 1, the common oil separator 32 comprises an inlet 70, fluidically connected to the compressor assemblies 30 so as to receive the compressed refrigerant from the compressor assemblies 30, a separation unit (not shown), configured to separate a second fraction of oil from the compressed refrigerant, a refrigerant outlet 72, through which the compressed refrigerant is intended to be discharged from the common oil separator 32 after separation of the second fraction of oil, and an oil outlet 74, through which the second fraction of oil is intended to be discharged from the common oil separator 32. More particularly, the refrigerant outlet 72 is fluidically connected with the outlet tube 22 of the cooling circuit section.

The common oil separator 32 may be of any other type adapted for separating oil from the refrigerant. More particularly, the common oil separator 32 is configured to separate the second fraction of oil from the refrigerant.

Preferably, for example in order to save cost, the individual oil separators 42 are of a different type than the common oil separator 32. In particular, the individual oil separators 42 are configured to separate a significantly smaller amount of oil from the refrigerant than the common oil separator 32.

The common oil separator 32 is, for example, a coalescence oil separator.

The coalescence oil separator is an oil separator configured to operate according to the coalescence principle. The coalescence principle is the accumulation of droplets of two identical substances which are dispersed in a fluid by reunification of the identical substances.

In an alternative embodiment, the common oil separator 32 is a centrifugal oil separator.

The centrifugal oil separator is an oil separator configured to separate oil from the refrigerant by centrifugation. In particular, due to the density difference between the oil and the refrigerant, the oil is separated by means of a rotating cylinder inside the centrifugal oil separator. Such centrifugal oil separators are known in the art.

The cooling circuit section 2 further comprises a common feedback tube 76 fluidically connecting the common oil separator 32 to each of the compressors 40 so as to feed the second fraction of oil back to the compressors 40.

In particular, the oil outlet 62 of the common oil separator 32 is fluidically connected, via the common feedback tube 76, to the inlet tube 20 of the cooling circuit section 2.

In the example shown in the figures, the common feedback tube 76 comprises an expansion device 78 configured to decrease the pressure of the second fraction of oil from the second pressure to the first pressure. In the example shown in the figures, the expansion device 78 is an expansion valve. However, any other adapted expansion device may be used, for example a capillary tube.

In the example shown in FIG. 1, the cooling circuit section 2 forms part of a cooling circuit 1, further comprising a heat exchanger device 80, an expansion valve 81 and an evaporator device 82.

The cooling circuit section 2 and the heat exchanger device 80 may, for example, form a condenser unit. The condenser unit is configured to compress and to condense the refrigerant.

The condenser unit is, for example, configured to be installed distant from the evaporator device. For example, in the case of a cooling circuit 1 implemented in a supermarket, the condenser unit may be installed in an equipment room and the evaporator device 82 in a customer area.

The heat exchanger device 80 comprises an inlet 83, fluidically connected to the outlet tube 22 of the cooling circuit section 2, an outlet 84 and a heat exchanging unit (not represented) arranged there-between.

For example, the heat exchanging unit comprises tubes which are fluidically connected to the inlet 83 and the outlet 84 and at least one fan configured to provide an air circulation across the tubes.

According to one example, the refrigerant is intended to enter the heat exchanger device 80 in a gaseous state.

The heat exchanger device 80 is configured to cool the refrigerant. In particular, the heat exchanger device 80 is configured to reject heat from the refrigerant into the environment of the heat exchanger device 80. The refrigerant at the outlet 84 has a temperature strictly smaller than a temperature of the refrigerant at the inlet 83.

According to one embodiment, the heat exchanger device 80 is a condenser. In this case, the heat exchanging unit is a condensation unit. The condenser is configured to cool the refrigerant in such a manner that the refrigerant condenses from a gaseous state into a liquid state. The condenser is, in this example, configured to cool a refrigerant at a pressure inferior to a critical pressure point. In this embodiment, the refrigerant is intended to exit the heat exchanger device 80 in a liquid state.

In another example, the heat exchanger device 80 is a gas cooler. The gas cooler is configured to cool the refrigerant in such a manner that it remains in the gaseous state. In this case, the refrigerant is intended to exit the heat exchanger device 80 in a gaseous state.

According to one example, the refrigerant is carbon dioxide and the heat exchanger device 80 operates with the refrigerant in a supercritical state. In particular, the refrigerant has for example a pressure greater than 73 bar. In this example, the heat exchanger device 80 is configured to provide the refrigerant in a supercritical gaseous state at the outlet 84.

The outlet 84 of the heat exchanger device 80 is fluidically connected to an inlet 85 of the expansion valve 81. The expansion valve 81 is configured to expand the refrigerant. It is configured to decrease the pressure of the refrigerant from the second pressure to the first pressure.

An outlet 86 of the expansion valve 81 is fluidically connected to the evaporator device 82.

The evaporator device 82 comprises an inlet 88, an outlet 90 and an evaporator unit (not represented) arranged there-between. For example, the evaporator device 82 comprises heat exchange tubes (not represented).

The evaporator device 82 is configured to evaporate the refrigerant by heat exchange between the refrigerant circulating through the evaporator device 82, and more particularly in the heat exchange tubes, and a cooling volume (not represented). The cooling volume is for example an inside of a refrigerator, a freezer, a cooling cabinet such as multideck cabinet, for example in a supermarket, or self-service counter, for example in a supermarket, a cold room or a refrigerated warehouse.

The outlet 90 of the evaporator device 82 is connected to the inlet tube 20 of the cooling circuit section 2.

The cooling circuit section according to the invention is particularly advantageous. In particular, the combination of individual oil separators 42 and a common oil separator 32 allows for a safe operation of the system, and more particularly of the compressors, thanks to a simple and reliable management of the oil management in the cooling circuit section.

In particular, within the cooling circuit 1 of the invention, the oil level in each compressor 40 is automatically maintained at a safe operational level, as each compressor 40 receives, via the individual feedback tube 44, a fraction of oil released into the refrigerant during compression of the refrigerant by the compressor 40.

For example, if one of the compressors 40 operates at a high frequency, a high amount of oil is released into the compressed refrigerant in this compressor 40. The corresponding individual oil separator 42 is then configured to feed back this large amount of oil directly into the corresponding compressor 40, in order to ensure that the compressor 40 disposes of enough oil for lubrication.

This is particularly important in the case of a hermetic compressor, in which, due to the hermetic closure of the casing, it is not possible to feed new oil into the compressor via its casing from outside of the cooling circuit.

Furthermore, the cooling circuit section 2 presents a very high efficiency for separating the oil from the refrigerant, since the cooling circuit 1 is configured to separate the oil from the refrigerant in two stages, namely in the individual oil separator 42 and the common oil separator 32. As a consequence, with the cooling circuit 1 of the invention, at the fluid outlet 72 of the common oil separator 32, no or almost no oil is left in the refrigerant after it leaves the common oil separator 32. The fact that the refrigerant circulating through the heat exchanger device 80 and the evaporator device 82 only contains very small amounts of oil is further advantageous, since it improves the thermodynamic performance of the refrigerant in the cooling circuit 1. 

1. Cooling circuit section, intended for the circulation of a refrigerant, said cooling circuit section comprising: at least two compressor assemblies, fluidically connected in parallel, each compressor assembly comprising: a compressor configured to receive a low-pressure refrigerant having a first pressure, and for increasing the pressure of the low-pressure refrigerant so as to produce a compressed refrigerant having a second pressure that is greater than the first pressure, the compressed refrigerant comprising oil, an individual oil separator comprising an inlet fluidically connected to the compressor so as to receive the compressed refrigerant from the compressor, each individual oil separator being configured to separate a first fraction of oil from the compressed refrigerant, the individual oil separator further comprising: a refrigerant outlet, through which the compressed refrigerant is intended to be discharged from the individual oil separator after separation of the first fraction of oil and an oil outlet, through which the first fraction of oil is intended to be discharged from the individual oil separator, the individual oil separator being further configured to return the first fraction of oil to the compressor, the cooling circuit section further comprising a common oil separator fluidically connected to the refrigerant outlet of each individual oil separator so as to receive the compressed refrigerant from each of the compressor assemblies, the common oil separator being configured to separate a second fraction of oil from the compressed refrigerant.
 2. Cooling circuit section according to claim 1, wherein the common oil separator comprises an inlet, fluidically connected to the compressor assemblies so as to receive the compressed refrigerant from the compressor assemblies, a refrigerant outlet, through which the compressed refrigerant is intended to be discharged from the common oil separator after separation of the second fraction of oil, and an oil outlet, through which the second fraction of oil is intended to be discharged from the common oil separator.
 3. Cooling circuit section according to claim 1, wherein the cooling circuit section further comprises a common feedback tube fluidically connecting the common oil separator to each of the compressors so as to feed the second fraction of oil back into the compressors.
 4. Cooling circuit section according to claim 3, wherein the common feedback tube comprises an expansion valve configured to decrease the pressure of the second fraction of oil from the second pressure to the first pressure.
 5. Cooling circuit section according to claim 1, wherein each compressor assembly comprises an individual feedback tube fluidically connecting the oil outlet of the individual oil separator to the compressor so as to feed the first fraction of oil back into the compressor of the compressor assembly.
 6. Cooling circuit section according to claim 1, wherein the individual feedback tube comprises an expansion device configured to decrease the pressure of the first fraction of oil from the second pressure to the first pressure.
 7. Cooling circuit section according to claim 1, wherein the common oil separator is a coalescence oil separator or a centrifugal oil separator.
 8. Cooling circuit section according to claim 1, wherein each of the individual oil separators is configured to separate the oil from the refrigerant based on differences in the densities of the refrigerant and the oil.
 9. Cooling circuit section according to claim 8, wherein the individual oil separators are chosen among a fluid speed decrease oil separator, configured to decrease the speed of the fluid fed into the oil separator and a fluid direction modification oil separator, configured to change the direction of the fluid fed into the oil separator.
 10. Cooling circuit section according to claim 1, wherein the compressor of each compressor assembly is a hermetic compressor.
 11. Cooling circuit section according to claim 1, wherein the refrigerant is carbon dioxide.
 12. Cooling circuit comprising a cooling circuit section according to claim 1, the cooling circuit further comprising a heat exchanger device configured to cool the refrigerant, an expansion valve and an evaporator device.
 13. Cooling circuit according to claim 12, wherein the heat exchanger device, the expansion valve and the evaporator device are connected in series, the heat exchanger device being connected to an outlet of the common oil separator and the evaporator device being connected to an inlet of the compressor assemblies.
 14. Cooling circuit according to claim 12, wherein the heat exchanger device is a condenser configured to cool the refrigerant such that the refrigerant condenses into a liquid state.
 15. Cooling circuit according to claim 12, wherein the heat exchanger device is a gas cooler configured to cool the refrigerant such that the refrigerant remains in the gaseous state.
 16. Cooling circuit section according to claim 11, wherein the refrigerant is carbon dioxide R744. 